1. Field of the Invention
This invention relates to the control of fungi.
2. Description of the Prior Art
Fungi which overwinter on a plant, especially inside the buds of the plant, are difficult to control as the fungus is already present on the plant in an active form at bud burst. Thus, for example, the fungus Podosphaera leucotricha (Ell. and Ev.) Salm. presents a major problem to commercial apple growers but, although the fungus has been known as the cause of a disease of apple and pear trees for nearly a century, none of the various methods which have been used in an attempt to combat the fungus have been successful in effecting more than a limited degree of control of the disease. A method has now been discovered employing certain fatty acids and fatty acid derivatives which has been found to give far better control of Podosphaera leucotricha and like fungi than it has previously been possible to achieve.
It is known that many of the compounds used in the method of the present invention exert a fungidical action against certain fungi as disclosed, for example, in the following papers: "Effects of vapours of aromatic chemicals on fungi," Journal of Pharmaceutical Sciences, 1961, 50, 665 - 668; "Antifungal properties of methyl esters of fatty acids and 2-fluoro fatty acids," Contributions from Boyce Thompson Institute, 1970, 24, 245 - 247; and "Action of odiferous organic chemicals and essential oils in wood-destroying fungi," Plant Disease Reporter, 1960, 44, 789 - 792. However, in the above references these compounds are shown to be wholly or partially inactive against a variety of fungi tested. The present discovery, therefore, that fungi which overwinter inside the buds of a plant or on other parts thereof, e.g. Podosphaera leucotricha and Venturia inaequalis, can now be controlled by these same compounds is clearly an unexpected and unpredictable result, which is even more unpredictable in view of the fact that all previous attempts to control these fungi have failed to a satisfactory degree.
It is also known that many of the compounds may be used on plants, including apples, as chemical pruning agents as disclosed, for example, in the papers "Plant growth inhibition by some fatty acids and their analogues," Nature, 1964, 202, 511 - 512; "Chemical pruning of plants," Science, 1966, 153, 1382 - 1383; and "Modern chemical pruning of plants," Florist and Nursery Exchange, Apr. 14, 1970, 6 - 13; and in the specifications of U.S. Pat. Nos. 3,326,664; 3,340,040; 3,438,765; and 3,620,712. However, the use of these compounds as chemical pruning agents is effective only on rapidly growing plants and it is specifically stated in these publications that dormant or resting plants exhibit no selective response to these compounds, so that no one would expect these compounds to have an important application out of the growing season.